LCDs are widely used in various modern information products, such as notebooks, personal digital assistants, video cameras and the like.
When motion pictures are displayed on an LCD, a so-called residual image phenomenon may occur. A motion picture is a series of images displayed one after another in rapid succession. In general, the displaying of each image lasts for a period of time known as a frame. Typically, each frame lasts a small fraction of a second. When a viewer is viewing an image of a current frame, the viewer may still be perceiving the image of the previous frame. That is the image of the previous frame remains in the viewer's perception as a so-called afterimage. The afterimage overlaps with the image of the current frame being viewed, and this causes the residual image phenomenon. From the standpoint of the viewer, the display quality of the LCD is impaired. To overcome the above-described problem, a method known as black insertion driving has been developed to drive an LCD.
FIG. 7 is an abbreviated circuit diagram of a conventional LCD. The LCD 100 includes a liquid crystal panel 101, a scanning circuit 102, and a data circuit 103. The scanning circuit 102 and the data circuit 103 are configured for driving the liquid crystal panel 101.
The liquid crystal panel 101 includes a plurality of parallel scanning lines 110, a plurality of parallel data lines 120 orthogonal to the plurality of parallel scanning lines 110, and a plurality of pixel regions 130 cooperatively defined by the crossing scanning lines 110 and data lines 120. The scanning lines 110 are electrically coupled to the scanning circuit 102. The data lines 120 are electrically coupled to the data circuit 103.
Each pixel region 130 includes a thin film transistor (TFT) 131, a pixel electrode 132, a common electrode 134, and liquid crystal molecules (not shown) interposed between the pixel electrode 132 and the common electrode 134. The TFT 131 is disposed near an intersection of a corresponding one of the scanning lines 110 and a corresponding one of the data lines 120. A gate electrode of the TFT 131 is electrically coupled to the corresponding scanning line 110, and a source electrode of the TFT 131 is electrically coupled to the corresponding data line 120. Further, a drain electrode of the TFT 131 is electrically coupled to the pixel electrode 132. The common electrode 203 is electrically coupled to a common voltage generating circuit (not shown) that is configured to provide common voltages. Moreover, each pixel electrode 132, the corresponding common electrode 134, and the liquid crystal molecules therebetween cooperatively form a liquid crystal capacitor 133.
Referring to FIG. 8 and FIG. 9, when the LCD 100 is driven by the black insertion driving method, each frame period is divided into a first sub-frame period T1 and a second sub-frame period T2. In particular, the first sub-frame period T1 serves as a normal display period, and the second sub-frame period T2 serves as a black frame insertion period.
During the first sub-frame period T1, a plurality of first scanning signals 150 are generated by the scanning circuit 102, and are sequentially supplied to the scanning lines 110, so as to scan the corresponding pixel regions 130 row by row. When the corresponding row of pixel regions 130 are scanned by the first scanning signal 150, the TFTs 131 of the pixel regions 130 are switched on. The data circuit 103 then supplies a plurality of first driving voltages to the pixel electrodes 132 of the pixel regions 130 via the data lines 120 and the TFTs 131. Thus, during the first sub-frame period T1, the LCD 100 displays a normal image 201.
During the second sub-frame period T2, the scanning circuit 102 supplies a plurality of second scanning signals 160 to switch on the TFTs 131 of pixel regions 130 row by row. The data circuit 103 supplies a plurality of second driving voltages having values the same as that of the corresponding common voltages supplied to the pixel electrodes 132 of the pixel regions 130. Thus, during the second sub-frame period T2, the LCD 100 displays a black image 202. The black image 202 includes a plurality of pixels (not labeled) arranged in a matrix, and all the pixels are black. Each of the pixels corresponds to one of the pixel regions 130 of the LCD 100.
By employing the black insertion driving method, normal images 201 and black images 202 are displayed alternately. In a complete frame period, a viewer perceives the normal image 201 during the first sub-frame period T1, and perceives the black image 202 during the second sub-frame period T2. Thus, an afterimage of the normal image 201 displayed in the first sub-frame period T1 is removed from the viewer's perception during the second sub-frame period T2. This means that the problem of the residual image phenomenon can be solved.
However, the black image 202 has the least brightness among all images displayed by the LCD 100. For example, in a continuous four frame periods, the LCD displays four normal images 201 and four black images 202. A time of displaying the four black images 202 is equal to that of displaying the four normal images 201. Thus, a brightness of images displayed by the LCD 100 is seriously reduced.
It is, therefore, desired to provide a method for driving an LCD which can overcome the above-described deficiencies.